The present invention relates to a fixing device applicable to an electrophotographic copier or like image forming apparatus for fixing a toner image which is provided on a paper and, more particularly, to a heat roller type fixing device having a fixing roller and a pressing roller which is rotatable in pressing contact with the fixing roller, and a method of producing the same.
A heat roller type fixing device is extensively used with a copier, facsimile apparatus, printer or similar image forming apparatus. An image forming apparatus includes a number of devices in addition to the fixing device. I conducted a series of experiments to find out an implementation for freeing images produced by an image forming apparatus from various kinds of defects. The experiments showed that one of major factors which effect an image is the characteristics of a heat roller type fixing device used. By studying various heat roller type fixing devices one by one, I found the following fact. When a pressing roller of a heat roller type fixing device is heated by a fixing roller, 3- to 15-mer low-molecular weight siloxanes (oligomers) are evaporated to adhere to other devices such as chargers (especially corona wires of chargers). The vapor of siloxanes adhered to chargers is burned to become silica (SiO.sub.2) which obstructs the discharge of the chargers. For example, SiO.sub.2 on a charger which is adapted to uniformly charge a photoconductive element lowers the total ability of the charger and/or renders the charge distribution irregular, resulting in an incomplete image. The current trend in the imaging art is toward a miniature image forming apparatus. In a miniature image forming apparatus, an ample space for oligomers evaporated from the pressing roller to be scattered is not available so that the amount of SiO.sub.2 deposited on the chargers and others is increased. It is to be noted that tetramer which is an example of the above-mentioned 3- to 15-mers has four Si--O and is expressed as: ##STR1##
The problem discussed above may be solved by a mechanical implementation such as coating the surface of the pressing roller with Teflon or causing oligomers to be entrained by a stream of air. However, this kind of implementation is not achievable without complicating the overall mechanism and increasing the cost.